1. Field of the Invention
This invention relates to a method of controlling positioning of a rotor of a stepping motor, and, in particular, to such a method which is suitable for use in a head actuator of a disc storage unit.
A stepping motor can precisely move a driven member or a rotor in steps and is therefore suitable for driving a head mechanism of a disc storage unit. As a result, most of the disc drive units recently developed employ stepping motors as the actuator means for the heads.
A rotor of a stepping motor however exhibits a hysteresis when driven in opposite directions, and a head carriage coupled to the rotor also has an inherent hysteresis characteristic. Those hysteresis characteristics result in an error in positioning of the head when the head is moved in both forward and reverse directions.
In a conventional disc storage unit, the control circuit of the stepping motor is so designed that the head is moved always in a predetermined direction before being positioned on desired tracks. More specifically, in the case of the predetermined direction being the inward direction (i.e., the direction from the outer side to the inner side of the disc), the head is moved in the inward direction when a track disposed inwardly of the current track is to be accessed. On the other hand, when a desired track is disposed outwardly of the current track, the head is first moved outwardly to a track disposed further outwardly of the desired track and then moved inwardly to access the desired track.
With this conventional method, however, the time required to seek a track disposed inwardly of the current track and that required to seek a track disposed outwardly of the current track differ from each other even when the distances from the current track to the inwardly and outwardly disposed tracks are equal to each other.